The objective of this proposal is to identify the regions of the insulin receptor molecule to which insulin binds and to identify their role in determining ligand specificity and in initiating signal transduction. Insulin resistance is commonly associated with glucose intolerance in humans, particularly with non-insulin dependent diabetes mellitus. Recently genetic defects of the insulin receptor have been shown to be responsible for certain syndromes of extreme insulin resistance. Thus understanding of the structure and function of the insulin binding site of the insulin receptor should provide further insights into the pathology of insulin resistance. Moreover knowledge obtained from this study could lead to the development of modified insulins with greater specificity for metabolic rather than mitogenic responses and with greater potency. Previous studied in this laboratory have identified an important role for phenylalanine 89 of the insulin receptor in insulin binding. This will serve as a starting point for the identification of more extensive regions of the receptor involved in insulin binding by site directed mutagenesis and the construction of chimeric molecules utilizing domains of the insulin and insulin-like Growth Factor I receptors. The specific aims of the proposed research are: 1. To identify regions of the receptor involved in insulin binding 2. To utilize site directed mutagenesis to define the roles of individual amino acids in insulin binding 3. To evaluate the role of the hetero-tetrameric receptor structure in high affinity ligand binding 4. To determine the roles of individual amino acids within the insulin binding region in initiating biological responses to insulin 5. To determine the role of the insulin binding site in suppressing receptor autophosphorylation and biological activity